This article gives comprehensive information about automated guided vehicles (AGVs).
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Automated Guided Vehicles (AGVs), commonly referred to as mobile robots, are flexible robotic systems that navigate along lines, across surfaces, or within designated areas. Unlike stationary robotic arms that are fixed to a base structure composed of joints and links, AGVs are autonomous and offer extensive movement and accessibility. Yet, when AGVs are paired with robotic arms, their capabilities are greatly amplified.
Combining AGVs with robotic arms results in a mobile workstation capable of executing a diverse array of tasks, such as remote manipulation, telemanipulation, scanning, and probing. AGVs find their utility in a wide range of sectors, including manufacturing, logistics, inspection, exploration, transport, and defense.
The technology behind AGV systems lies in the realm of automation, showcasing intricate control mechanisms and cutting-edge guidance systems that allow them to traverse long distances and be multifunctional. These systems incorporate navigation techniques such as perception, localization, path planning, and motion control, which can be coordinated through an onboard computer, a centralized computer system, or even a dispatcher.
The routes for AGVs are carefully designed to prevent any obstacles, blockages, or interferences that might disturb their activities. Furthermore, AGVs require a flat, smooth terrain to function efficiently, as they are not built to handle uneven surfaces like holes, bumps, or cracks.
The 2020 pandemic propelled AGVs into the spotlight due to the necessity for social distancing and the e-commerce boom. This surge in demand triggered advancements in more dependable and efficient AGV systems. Many factories integrated AGVs into their workflow to maintain social distancing while still maneuvering products, equipment, and necessary resources.
With the swift progression of AGV technology, the expansion of wireless connectivity has followed suit. AGVs depend on strong, dependable connectivity to guarantee seamless, efficient functionality during their operations.
AGVs are primarily utilized in logistics, with other functions such as exploration, inspection, and service robotics representing a smaller segment of the industry. As a result, automated guided vehicles are categorized based on their load capacity and mode of transport.
Forklift automated guided vehicles are simply automated guided vehicle navigation systems integrated into a forklift. They are suitable for floor-level pallet pick-up and can stack pallets at various heights. Forklift AGVs are widely used in automatic storage and sorting systems, particularly automatic warehouse racking. The navigation system can be overridden to allow manual control.
Underride Automated Guided Vehicles (AGVs), also known as Automated Guided Carts (AGCs), are designed to lift loads by driving underneath a basket or cart and raising it slightly. These AGVs can autonomously transport and deposit the load at its destination without manual intervention. They are commonly used in hospitals for delivering food, linens, and medical supplies.
Towing or tugger automated guided vehicles pull undriven carriers or trailers. Since their load-carrying does not involve lifting, they can handle multiple loads, in contrast with forklifts and underride AGVs. However, they are solely for transport and cannot position the loads to their location.
Unit load Automated Guided Vehicles (AGVs) are designed to transport unitized or palletized goods without lifting the load from the floor. Loading and unloading are typically handled by additional equipment such as conveyors, cranes, or forklifts.
Assembly Automated Guided Vehicles (AGVs), also known as tunneling AGVs, are specifically designed for transporting goods to assembly processes. In controlled assembly environments, their navigation is simpler and operates at lower speeds compared to other types of AGVs. These vehicles are highly maneuverable, enabling them to easily fit into and orient within assembly stations.
Tunneling AGVs pull a companion frame to a designated drop-off location. Upon arrival, the AGV may pass over an RFID puck, which triggers the vehicle's next action. Compared to forklift AGVs, assembly AGVs are more efficient and cost-effective, as they only require a companion frame to deliver assembly parts or components.
Heavy load Automated Guided Vehicles (AGVs) are commonly used in industries such as paper and steel mills to transport rolls of finished products for storage or distribution. These AGVs are built with a more robust construction compared to other types and are equipped with additional safety features to handle the demands of heavy-duty operations.
Mini Automated Guided Vehicles (AGVs), also known as small load carriers, are designed for transporting small parts or objects and often operate in swarms or fleets. They typically feature a three-wheel drive system, providing stability and a minimal turning radius, allowing them to move quickly and with high flexibility. These AGVs are commonly used in high-selectivity racking systems.
AGV scissor lifts are an ergonomic method for positioning large products during assembly. As a product arrives at a workstation, it is raised or lowered such that a worker does not have to reach or bend to add their portion of the assembly process. AGV scissor lifts can lift one or two tons as high as 50” for convenient and easy access.
When an assembly process is spread across various stations within a facility, an AGV scissor lift can be programmed to move between these stations, regardless of their location. Like other AGVs, scissor lifts can also be programmed to travel between rooms or deliver completed assemblies for storage or shipping. This capability enhances efficiency, reduces assembly time, and helps prevent worker injuries by handling heavy lifting and transport tasks.
Truck loading Automated Guided Vehicles (AGVs), also known as Automated Trailer Loading (ATL) AGVs, are designed to load and unload trucks without requiring guidance systems or modifications to the truck's trailer or the dock. These AGVs can handle pallets or unit loads in various patterns, including mixed orientations, and can operate over dock plates and other uneven surfaces, carrying loads of up to four pallets.
Equipped with lasers and natural targeting navigation systems, these AGVs can accurately navigate the interior of the trailer without needing alterations to the dock, trailer, or surrounding area.
Cobot is an inclusive term for a collaborative robot that can safely work with humans. They have sensitivity sensors that control their motions. If they sense an interruption in their motion, they stop and go into safety mode, unlike normal robots that will continue to operate and possibly injure people.
Integrating Automated Guided Vehicles (AGVs) with collaborative robots (cobots) enables them to handle a broad range of tasks. By leveraging the cobots' lifting strength alongside the AGVs' mobility, this combination effectively reduces repetitive strain and minimizes worker stress.
Key benefits of integrating AGVs and cobots include:
Navigation involves a guided vehicle or mobile robot's ability to determine its position and autonomously navigate to its destination while avoiding obstacles and unsafe conditions. This process consists of four key components: perception, localization, path planning, and motion control.
The process of acquiring data for mobile robot navigation is more complex and comprehensive compared to that of robotic arms. While mobile robots, like robotic arms, rely on sensors for perception, their higher sophistication comes from their capability to measure and relate their position both globally and across a broad range of environments.
Sensors are categorized along two functional axes: proprioceptive/exteroceptive and passive/active. Proprioceptive and exteroceptive sensors monitor the Automated Guided Vehicle (AGV) itself, while passive and active sensors interact with the surrounding environment by either receiving or emitting energy.
These sensors include contact switches and proximity sensors. They can measure through physical contact, such as limit switches, or through various physical phenomena like magnetism (reed and Hall effect switches) and electric induction (inductive switches).
These sensors include compasses and gyroscopes. Heading sensors are utilized to determine the robot's orientation relative to a fixed external reference point or frame.
-gyroscope.jpg "AGV Micro-electromechanical System (MEMS) Gyroscope")
Wheel and motor sensors measure the angular position, speed, and acceleration of a motor or wheel. For instance, an encoder in a servo motor provides feedback signals that are used to control the motor drive.
These sensors measure the robot's speed relative to a fixed or moving object. Unlike proprioceptive wheel and motor sensors, these are exteroceptive sensors.
These sensors measure the robot’s acceleration, although acceleration is often less critical than other measurements. Position can be indirectly calculated from acceleration, initial position, and orientation using dead reckoning. Typically, a combination of acceleration and heading sensors is known as an Inertial Measurement Unit (IMU).
These sensors use a known fixed reference point or frame to determine a robot’s position and orientation. For example, the Global Navigation Satellite System (GNSS) employs an electronic receiver that receives orbital data from three or more satellites. By comparing this data with the time-of-flight measurements, the system calculates the robot's position and orientation.
Active ranging sensors are capable of both transmitting and receiving signals. They emit a signal towards an object or reference point, which reflects back to the sensor. The returned signal is then measured and analyzed using concepts such as reflectivity, time-of-flight, and triangulation. Examples of active ranging sensors include lidar, radar, and sonar.
Vision is a high-level capability that enables robots to analyze captured images for localization. Additionally, vision systems can perform tasks such as obstacle avoidance and object recognition.
After gathering information from the environment or a fixed reference frame, the robot processes this data to determine its position and orientation relative to its surroundings through a process called localization. A robot’s position and orientation can be established using odometry (dead reckoning) or triangulation from fixed reference points. However, these methods often fall short when high accuracy is required.
The environment frequently contains unknown obstacles and dynamic restrictions, while sensors and effectors may have issues with accuracy and precision. To achieve full autonomy and advance to subsequent navigation steps, the robot uses mapping to create a model of the environment. This model helps the robot determine its location, orientation, and goals, and allows for real-time updates in a process known as Simultaneous Localization and Mapping (SLAM).
Path planning involves determining the sequence of actions required for the robot to reach its destination. This cognitive process involves analyzing the map of the environment and generating a program or set of instructions. If changes occur in the environment, the robot must detect these alterations and adjust its actions accordingly. Additionally, path planning not only involves finding a route to the target location but also optimizing it by minimizing the path length and avoiding obstacles.
Path planning involves four key concepts: the robot's geometry, the degrees of freedom of its effectors, the map of the environment, and the initial and target configurations. To address the robot’s path planning, these concepts are translated into what is known as the configuration space. In this space, both the robot’s possible configurations and the space occupied by obstacles are represented. The robot is modeled as a point defined by coordinate vectors rather than a rigid body. Consequently, obstacles are effectively "inflated" by the robot’s size to account for its dimensions. By understanding the possible configurations of all objects on the map, the robot’s trajectory can be determined as a continuous curve or path.
Motion control involves executing a robot's planned or programmed actions by sending input signals to its drivers, actuators, and effectors. For mobile robots, the control system is typically a closed-loop system. The most common closed-loop control in robotics is Proportional-Integral-Derivative (PID) control, a type of feedback control. This feedback mechanism allows the robot to correct deviations or errors in its trajectory by continuously monitoring both internal and external parameters. The PID controller mathematically computes the error signal and adjusts the proportional, integral, and derivative gains to quickly minimize errors while maintaining stability and avoiding overshoot.
Zone blocking is managed by a central AGV system controller, which permits only one AGV to enter any given zone at a time. This approach is employed in areas of the guide path that feature intersections, stations, and turns. By controlling access to these high-traffic zones, zone blocking facilitates the smooth release of multiple vehicles into busy intersections while preventing potential interference between them.
In accumulative blocking, AGVs are regulated by remote object detection sensors rather than a central system. This method is utilized on long, straight sections of guide paths where AGVs can detect slower-moving or stationary vehicles ahead. With accumulative blocking, AGVs gather or queue behind one another as they advance towards the next intersection. This approach is generally faster and more efficient compared to zone blocking.
The complete navigation system is developed through the integration of perception, localization, path planning, and motion control processes. Additionally, various navigation systems can be designed by combining different sensors, controllers, software programs, and algorithms. Below are some of the most commonly used navigation systems for automated guided vehicles.
Physical guides include guide tracks, tapes, and wires that are detected either actively or passively. This navigation system relies on fixed reference points or environmental landmarks, which are measured and interpreted by sensors and controllers. Because the automated guided vehicle (AGV) follows predetermined paths, its path planning can be preprogrammed into its system.
One example is the inductive guide track, or wire guidance system, which involves embedding a current-carrying conductor into the ground or floor. The tracks are sectionalized into segments that can be individually activated or deactivated. An alternating current flows through the wire, generating electromagnetic waves that are detected by sensors mounted on the AGV. These sensors, which contain two coils, detect the induced currents and convert them into analog signals that are sent to the feedback controller.
Examples of physical guides also include magnetic, metallic, and optical guide strips. These strips are applied to the floor and detected by various sensors mounted on the AGV. Magnetic proximity sensors use the Hall effect to identify magnetic materials, while inductive proximity sensors rely on electromagnetic induction to detect metallic objects. Optical sensors, on the other hand, recognize the guide strips by their color or other visual features. While physical guides are generally more cost-effective and easier to reconfigure than wire guidance systems, they may not perform well in dirty environments or high-traffic areas.
Anchoring points are another form of physical guide that enable more flexible navigation. Instead of using fixed paths like wires or tapes, a grid of permanent magnets or transponders is placed on the floor. These guides help the automated guided vehicle (AGV) determine its location and orientation. Magnetic proximity sensors mounted on the AGV detect these anchors, allowing the vehicle to follow a path based on preprogrammed routes or dynamic path planning.
Laser navigation is a versatile system that employs active-ranging light sensors for precise localization. Reflective markers, such as foils or tapes, are placed on walls or objects, making them easily detectable by the laser sensor. At least three markers are required for accurate triangulation. This system allows the automated guided vehicle (AGV) to perform both localization and path planning, offering a high degree of flexibility in its trajectory and enabling the computation of the most efficient path.
GPS navigation is employed in outdoor environments where placing artificial markers is impractical. The system uses GPS satellites as beacons, sending data to the automated guided vehicle (AGV) to triangulate its position. However, relying solely on GPS can be problematic due to its lower accuracy, particularly indoors. To ensure reliable performance, there must be an unobstructed line of sight between the satellite and the AGV.
The growing adoption of AGV systems has heightened the demand for dependable connectivity solutions to support swift and efficient operations. When designing and planning a wireless connectivity system, several key factors must be considered to ensure optimal reliability.
In manufacturing environments, factors like electrical interference from ground loops and conveyor belts can disrupt AGV performance. Additionally, vibrations from AGV operation can also impact functionality. To mitigate these issues, wireless navigation systems must incorporate radio frequency (RF) and power isolation to protect against electrostatic discharge and motor current surges.
Robust protective features ensure that AGVs maintain stable wireless connections even in electrically active and harsh environments. These measures not only enhance reliability but also extend the operational lifespan of the AGVs.
AGVs, due to their roaming technology, continuously search for and switch to access points with stronger signals. It is crucial to provide an environment that facilitates smooth transitions between access points and ensures seamless connectivity.
Wi-Fi coverage plays a key role in determining how quickly an AGV can connect to an access point. Wireless devices with multiple input and multiple output (MIMO) capabilities can enhance coverage and reduce the need for additional access points.
Choosing the right wireless communication system is essential for integrating AGV systems smoothly. The first step is to configure the wireless local area network (WLAN) settings appropriately. Additionally, equipping AGVs with external antennas can improve their Wi-Fi coverage.
Despite taking precautions, environmental obstacles such as walls, pillars, or large equipment can still cause interference, hindering access point detection and potentially leading to collisions. Implementing a request to send and clear to send (RTS/CTS) mechanism can help prevent these issues and avoid collisions.
Securing the wireless network with appropriate security protocols is vital to prevent unauthorized access, which could disrupt system operations. All wireless communication devices should be secured to restrict access to authorized personnel only. Management software can help monitor the network environment and control access to connections, ensuring overall network security.
Locomotion refers to the capability of automated guided vehicles (AGVs) to move from one location to another. Wheels are a popular choice for locomotion due to their simplicity and low friction. However, wheeled AGVs can struggle on irregular or uneven surfaces. In such environments, legged robots are often preferred due to their ability to navigate challenging terrain more effectively.
Wheels are a widely used technology in robotics, valued for their efficiency and straightforward mechanical design. They offer a high degree of freedom, stability, and excellent maneuverability. In the context of robotics, wheels can be categorized based on their kinematic properties. Below are the various types of wheels commonly employed in automated guided vehicles.
Wheels are a widely used technology in robotics, valued for their efficiency and straightforward mechanical design. They offer a high degree of freedom, stability, and excellent maneuverability. In the context of robotics, wheels can be categorized based on their kinematic properties. Below are the various types of wheels commonly employed in automated guided vehicles.
As with the standard wheel, a caster wheel offers two degrees of freedom. One is rotation around the wheel axis, while the other is around an offset from the center of the wheel. Caster wheels are generally used to provide support for the chassis. It is rarely used for maneuvering and delivering motion since steering using caster wheels exerts forces on the chassis. The main advantage of using caster wheels is their automatic alignment when moving forward after turning.
Also known as Swedish wheels, Mecanum wheels offer three degrees of freedom: rotation around the wheel axis, rotation around the rollers, and rotation at the contact point. These wheels feature rollers mounted at 45° angles around the wheel's circumference. Another type of omnidirectional wheel has rollers positioned at 90° angles. To enable omnidirectional movement, an AGV typically uses three or more Mecanum wheels mounted on its chassis, which rotate in both clockwise and counterclockwise directions.
Spherical wheels provide three degrees of freedom, allowing rotation around all three axes. While the concept of true spherical wheels is intriguing, their practical implementation in large chassis presents challenges such as conflicting rotations between drivers, lack of unpowered stability, and complications in power transmission systems.
To achieve the desired stability and maneuverability, various wheel configurations can be combined. A statically stable robot requires at least two wheels, with stability ensured by lowering the robot's center of mass below the wheel axle. For robots with three or more wheels, stability is maintained by keeping the center of mass within the polygon formed by the wheel contact points on the ground. Common configurations include two-wheel drives with one or two undriven wheels for steering, often using a differential for maneuvering. Four-wheel drives can utilize two pairs of driven and steered wheels or four individually driven and steered Mecanum wheels for enhanced maneuverability.
A legged AGV is a type of terrestrial automated guided vehicle designed for high maneuverability on uneven terrain. It can traverse gaps or holes if its legs extend beyond the width of the gap. Despite its advantages, legged AGVs are less common in industrial settings due to limitations in load-carrying capacity and the complexity of their mechanical systems. Each leg comprises multiple links and joints, often requiring independent actuators. The increased number of actuators adds weight, reducing the robot's payload capacity, and necessitates additional power and control systems. Consequently, much of the development effort for legged AGVs is focused on optimizing the leg kinetics and control mechanisms rather than on other aspects like navigation and localization.
Aerial automated guided vehicles (AGVs) operate on different principles of flight and can be classified into two main categories: Lighter Than Air (LTA) and Heavier Than Air (HTA). LTAs include balloons and blimps. Balloons offer limited control, primarily for elevation, while blimps are equipped with propellers for lateral movement. HTAs encompass gliders, planes, and rotorcrafts. Gliders and planes use wings and airfoils to interact dynamically with the air, while rotorcrafts use rotary blades or propellers to generate lift and move laterally. Among these, rotorcrafts, such as unmanned aerial vehicles (UAVs) or drones, are the most practical and versatile. They are lightweight, compact, and easy to control, with the added benefit of vertical takeoff and landing. Drones are widely used for various applications, including photography, inspection, navigation, and agriculture.
Submersible automated guided vehicles, or autonomous underwater vehicles (AUVs), operate on principles similar to aerial AGVs. AUVs are comparable to blimps in that they use buoyant force to stay afloat and employ rotor blades for lateral movement. These vehicles are utilized in various scientific and industrial applications, including seafloor mapping, environmental monitoring, and inspections of pipelines and cables.
Roll handling automated guided vehicles (AGVs) are designed to transport large rolls of paper, plastic, or steel coils. These vehicles retrieve and deposit rolls at designated locations. They feature forks that extend towards the rear of the vehicle, lifting the roll two to four inches off the ground. Once elevated, the AGV moves the roll to its assigned destination. Roll handling AGVs typically handle loads weighing up to four tons, with roll diameters ranging from 60 to 110 inches (152.4 to 279.4 cm).
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